In the past, many municipal waste treatment plants have not operated reliably. A 1969 Federal Water Pollution Control Administration Study, for instance, showed that 25% of 1500 plants examined had experienced mechanical difficulties; of these, 38% found it necessary to bypass untreated sewage into receiving streams. In nearly half the cases of plant failure, the cause was attributed to inadequate design. Besides giving six examples of poor plant design — with proposed better designs—this article tells of EPA'S recent efforts to improve plant reliability. Recently, EPA published design criteria to improve plant reliability. A recent EPA-sponsored study not only indicates that the new criteria will eliminate or greatly reduce plant failure in most plants; but will boost plant cost only 1 to 7%.